The regular expression in perl one liner not giving the expected output

perladdict has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks,
I have file with contents
root@phaniraj ~]# cat p1
usmat-d0209.mail.aol.com
CentOS release 4.7 (Final)
usmat-d0210.mail.aol.com
CentOS release 4.7 (Final)
usmat-d0211.mail.aol.com
CentOS release 4.7 (Final)
usmat-d0212.mail.aol.com
CentOS release 4.7 (Final)
usmat-d0213.mail.aol.com
CentOS release 4.7 (Final)

I want to modify file to get output like

usmat-d0209.mail.aol.com CentOS release 4.7 (Final)
usmat-d0210.mail.aol.com CentOS release 4.7 (Final)
usmat-d0211.mail.aol.com CentOS release 4.7 (Final)
usmat-d0212.mail.aol.com CentOS release 4.7 (Final)

[root@phaniraj ~]# cat p1 | perl -p -e 's/^(usmat.*)\n(.*)/$1 phani $2
+ raj/m '
[download]

From the above code i am getting result as
usmat-d0209.mail.aol.com phani rajCentOS release 4.7 (Final)
usmat-d0210.mail.aol.com phani rajCentOS release 4.7 (Final)
usmat-d0211.mail.aol.com phani rajCentOS release 4.7 (Final)
usmat-d0212.mail.aol.com phani rajCentOS release 4.7 (Final)
usmat-d0213.mail.aol.com phani rajCentOS release 4.7 (Final)

It is not matching second line properly

Comment on The regular expression in perl one liner not giving the expected output Download Code

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Re: The regular expression in perl one liner not giving the expected output by jwkrahn (Abbot) on Feb 03, 2010 at 07:34 UTC
The `-p` switch on the command line tells perl to read one line at a time therefore the contents of `$2` are always empty because there is nothing after the newline for it to match. You need something like: `perl -lpe'$\ = /^usmat/ ? " phani " : " raj\n"' p1` [download]	[reply] [d/l] [select]
Re: The regular expression in perl one liner not giving the expected output by CountZero (Bishop) on Feb 03, 2010 at 07:01 UTC
Do not use `</br>` tags. Please put your data also in `<code> ... </code>` tags. That makes it a lot easier to look at it or download it to test it. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply] [d/l] [select]
Re: The regular expression in perl one liner not giving the expected output by JavaFan (Canon) on Feb 03, 2010 at 09:06 UTC
Untested: `perl -pe 's/\n/ / if /^usmat/'` [download]	[reply] [d/l]